typical examples of the compounds represented by the foregoing formula i include : according to the present invention , the foamable resin composition should contain at least 0 . 1 percent by weight , based on the aliphatic olefin polymer , of at least one compound represented by the formula i , with the total content thereof falling in the range of 0 . 1 to 10 percent by weight when two or more such compounds are used . the amount of compound or compounds added may be selected within this range depending on the types of polymer and blowing agent used as well as on the shape , physical and mechanical properties of the intended foam . generally , it is preferable that the total amount of the formula i compound employed be in the range of 0 . 3 to 7 percent by weight . if the content of the formula i compound is smaller than 0 . 1 percent by weight , the reultant foam will generally have inferior properties . on the other hand , using more than 10 percent by weight of the formula i compound generally give no further improvement and may show undesirable plasticizing action . the aliphatic olefin polymers herein referred to are normally solid polymers predominantly composed of olefins , including low - density polyethylene , medium - density polyethylene , high - density polyethylene , isotactic polypropylene and poly - 1 - butene and such copolymers of ethylene or propylene and other monomers copolymerizable therewith as propylene -( 1 - octene )- ethylene copolymer , ethylene - propylene copolymer , ethylene - vinyl acetate copolymer , ethylene - acrylic acid copolymer , ethylene - ethyl acrylate copolymer and ethylene - vinyl chloride copolymer as well as zinc , sodium , calcium and magnesium salts of ethylene - acrylic acid copolymer . these aliphatic olefin polymers may be used individually or as mixtures of two or more . for mixing the formula i compound ( s ) of the present invention with the aliphatic olefin polymer to be employed , such components may be admixed and kneaded by any suitable conventional means such as single - screw extruder , twin - screw extruder , compounding rolls , and banbury mixer . in any case , a preliminary blend of the formula i compound ( s ) and the olefin polymer may be prepared as a dryblend or masterbatch , or the formula i compound may be mixed with the olefin polymer in molten or heat plastified form just before expansion . the foamable olefin polymer composition of the present invention may be expanded into a foam by conventional methods . thus , for example , conventional extrusion foaming techniques can be employed in which an admixture of the olefin polymer and the formula i compound ( s ) of the present invention is continuously heated and / or worked to be melted or heat plastified and a volatile organic blowing agent is added thereto at an elevated temperature under high pressure . then , the resultant molten or heat plastified mixture is extruded into a lower - pressure zone to be expanded into a foam . alternatively , a batch method may be used , in which the volatile organic blowing agent is added at elevated temperature under high pressure to a molten composition comprising the olefin polymer and the formula i compound and , then , pressure is removed from the molten mixture system . also the olefin polymer / formula i compound composition can be crosslinked with electron beams or a chemical crosslinking agent if desired before expansion . however , the present invention is particularly effective when applied to extrusion - expansion of olefin polymer compositions and especially when such compositions are to be expanded to five or more times their original , unexpanded volume . any conventional volatile organic blowing agents may be used as desired . however , especially preferable for use in the present invention are those volatile organic blowing agents that have boiling points lower than the melting point of the aliphatic olefin polymer employed . typical examples of such preferable blowing agents include propane , butane , pentane , pentene , hexane , hexene , heptane and octane . also usable as the blowing agents are such halogenated hydrocarbons meeting the foregoing limitation on the boiling points as methylene chloride , trichlorofluoromethane , dichlorofluoromethane , chlorodifluoromethane , chlorotrifluoromethane , dichlorodifluoromethane , 1 , 1 - dichloroethane , 1 - chloro - 1 , 1 - difluoroethane , 1 , 8 - dichlorotetrafluoroethane , chloropentafluoroethane and the like , including mixtures thereof . in addition to such volatile organic blowing agents , known chemical blowing agents such as azodicarboniamide , azobisisobutyronitrile , dinitrosopentamethylenetetramine , p - toluenesulfonyl hydrazide and the like can also be optionally employed in conjunction the aforementioned volatile organic blowing agents . the expandable or foamable olefin polymer composition according to the present invention may contain minor amounts of lubricating and nucleating agents such as zinc stearate or similar metal soaps and finely - ground calcium silicate or the like inorganic materials . also , the resin composition of the present invention may contain an ultraviolet light absorber , antistatic agent , stabilizer , colorant and / or lubricating agent other than the foregoing in a total amount not exceeding 5 percent by weight . the foamable aliphatic olefin polymer compositions according to the present invention may be expanded into almost any shapes including sheets , blocks , rods and pipes , or it may be used for electric wire and cable coverings or sheathings or as a variety of other formed foam articles . the present invention is further illustrated by the following examples and the accompanying comparative or reference experiments . in such examples and comparative ( or reference ) experiments , the effects of the present invention were evaluated in terms of the hereinafter described properties and parameters . also , in such examples and experiments , all parts and percentages are given on a weight basis unless otherwise specified . ( a ) the 25 % compressive strength ( in kg / cm 2 ) was measured according to jis - k - 6767 . ( b ) the compressive strength coefficient ( a ) was determined by applying the 25 % compressive strength ( p ) to the following formula : y =( 1 -( α / 100 ), with α representing the comonomer content , if any ( wt . %) of the olefin polymer employed . 2 . the 50 % compression permanent set was measured in accordance with jis - k - 6767 . 3 . the compressive creep was measured in accordance with jis - k - 6767 ( static load : 0 . 1 kg / cm 2 , 24 hrs ). for evaluating the surface smoothness of a foam , the coarseness of the specimen was measured over a 10 cm length on its surface by means of a coarseness meter which detects and counts rippling creases or concavo - convexes not smaller than 0 . 5 mm in their amplitudes , and the count was converted into a value per 1 cm in length . each resin composition was extruded through an extruder of 30 mm in its barrel diameter and the throughput per minute was measured to determine its percentage variation by the following formula : ## equ1 ## the volume of each expanded foam specimen was measured by the water - immersion method within one minute after expansion and t days thereafter , respectively , and the measurements were applied to the following formula to determine the percentage shrinkage : v o : volume measured within one minute after expansion the maximum percentage shrinkage was used as a measure of foam specimen evaluation . the dimensional stability was calculated by applying the measurements of the preceding paragraph 6 to the following formula : wherein v 20 is the volume of the foam specimen measured 20 days after expansion . the volume ( v ) and weight ( w 0 ) of a foam specimen about 100 mm × 100 mm × 25 mm ) were accurately measured , and the foam specimen was immersed in water contained in a vacuum chamber with its top placed at a depth of 5 cm below the surface . then , after reducing the internal pressure of the chamber to 460 mm hg , the specimen was left to stand in the water for 10 minutes . thereafter , the internal pressure of the chamber was restored to the atmospheric pressure , and the specimen was taken out from the chamber and immersed in methanol having the purity of 95 % or more for 2 seconds . after air drying the thus treated specimen for 5 minutes at 60 ° c ., its weight ( w 1 ) was accurately measured . the measurements w 0 , w 1 and v were applied to the following formula to determine the closed cellular characteristic value : each evaluation item was applied to each specimen in accordance with the following schedule : __________________________________________________________________________ evaluation a b c d evaluation item ( excellent ) ( good ) ( passable ) ( bad ) __________________________________________________________________________ compressive 8 . 0 × 10 . sup .- 3 4 . 0 × 10 . sup .- 3 2 . 15 × 10 . sup .- 3 less than strength or more or more , but or more , but 2 . 15 × 10 . sup .- 3 coefficient less than less than 8 . 0 × 10 . sup .- 3 4 . 0 × 10 . sup .- 3 50 % compression from 0 to 5 to less 15 to less 30 or more permanent set (%) less than 5 than 15 than 30 compressive creep from 0 to 5 to less 10 to less 20 or more (%) less than 5 than 10 than 20 surface smoothness from 0 to 3 to less 6 to less 10 or more ( number / cm ) less than 3 than 6 than 10 feedability from 1 to 5 to less 10 to less 15 or more through extruder less than 5 than 10 than 15 (%) maximum shrinkage from 0 to 10 to less 15 to less 20 or more (%) less than 10 than 15 than 20 dimensional from 0 to 5 to less 10 to less 15 or more stability (%) less than 5 than 10 than 15 water absorption from 0 to from 0 . 010 from 0 . 025 0 . 50 or more ratio ( g / cm . sup . 3 ) less than to less than to less than 0 . 010 0 . 025 0 . 050__________________________________________________________________________ for overall evaluation , all of the foregoing evaluation items 1 through 8 were taken into consideration in a combined manner as follows : ______________________________________e ( excellent ) specimens having at least two excellent marks ( a ) and no pass - able ( c ) or bad ( d ) marks . g ( good ) specimens having at least one good mark ( b ) with one or two passable marks ( c ) and without any bad marks ( d ). f ( fair ) specimens having at least three passable marks ( c ) without any bad marks ( d ). p ( poor ) specimens having at least one bad mark ( d ). ______________________________________ in the following examples and reference experiments , the following aliphatic olefin polymers , volatile organic blowing agents and additives were used . resin a : low - density polyethylene produced by asahi - dow limited , with density of 0 . 919 g / cm 3 and mi of 2 . 0 g / 10 minutes . resin b : ethylene - vinyl acetate ( eva ) copolymer produced by sumitomo chemical co ., ltd ., with vinyl acetate content of 10 %, density of 0 . 93 g / cm 3 and mi of 1 . 5 g / 10 minutes . resin c : ethylene - vinyl acetate copolymer produced by sumitomo chemical co ., ltd ., with vinyl acetate content of 25 %, density of 0 . 95 g / cm 3 and mi of 1 . 5 g / 10 minutes . 100 parts of the aliphatic olefin polymer a , b , or c , the additive i or ii in an amount shown in table 1 , 0 . 1 part of calcium stearate and 0 . 6 part of calcium silicate as nucleators and 22 parts of the blowing agent d , e , f , or g were fed into a 30 mm inside barrel diameter single - screw extruder , the barrel being heated to 190 ° c ., provided with a die having a round aperture of 5 mm diameter . each of the resultant polymer compositions was melted and kneaded in the extruder and was extruded through the die to be expanded into a foam . during the extrusion , the polymer composition temperature was controlled to 105 ° c . within the die . the resultant foam was subjected to evaluation in terms of the aforementioned evaluation items , the results of which are shown in table 1 . as reference experiment 1 , the same procedure and conditions as those used in example 1 were repeated , except that either no additive was used or the additive iii was used in place of additives i and ii and except that the base resin c was not used . like example 1 , each foam obtained in reference experiment 1 was evaluated in terms of the aforementioned items and the results of such evaluations are also shown in table 1 . fig1 and 2 shown changes in the volume and weight of the foam specimens of formulation 1 in example 1 and of formulation 1 in reference 1 as a function of time after expansion . as can be clearly seen from fig1 the additive of formulation 1 in example 1 is highly effective to prevent shrinkage of the formulation 1 , example 1 foam product . table 1__________________________________________________________________________ base additive blowing evaluation items resin ( part ) agent density 1 2 3 4 5 6 7 8__________________________________________________________________________example 1 . sup .+ formulation 1 a i 0 . 5 d 0 . 030 a a a a a a a aformulation 2 a i 1 . 5 e 0 . 032 a b b b a b a aformulation 3 a i 4 . 0 f 0 . 034 a b b b b b a aformulation 4 b i 1 . 0 d 0 . 029 a b b a a a a aformulation 5 c ii 1 . 5 d 0 . 031 a b b a a a a aformulation 6 c ii 2 . 5 e 0 . 033 a b b a b b a aformulation 7 c ii 1 . 0 g 0 . 037 a b b a a a a areference 1 . sup .+ formulation 1 * a none d 0 . 040 c b b d a d b aformulation 2 * a iii 2 . 0 d 0 . 040 c b b d a d b aformulation 3 * b none d 0 . 080 c c d d a d b bformulation 4 * b none g 0 . 088 d d d d a d d b__________________________________________________________________________ . sup .+ the overall evaluation of example 1 , formulations 1 - 7 was excellen and of reference 1 , formulations 1 - 4 was poor . * not an example of the invention . evaluation item 1 compressive strength coefficient ; 2 50 % compression permanent set ; 3 compressive creep ; 4 surface smoothness ; 5 feedability through extruder ; 6 maximum shrinkage ; 7 dimensional stability ; and 8 water absorption ratio . as example 2 , the same procedure and conditions as those used in example 1 were repeated by using the olefin polymer resin b , additive i and blowing agent d as used in the formulation 4 of example 1 , except that the amounts of the additive i and blowing agent d were changed as shown in table 1 . in reference experiment 2 , the same procedure and conditions as those used in reference 1 , were repeated , without additive , by using the olefin polymer resin b and blowing agent d as used in the formulation 3 of reference 1 , except that the amount of the blowing agent was changed as shown in table 2 . like example 1 , the resultant foams of example 2 and reference experiment 2 were subjected to evaluation , the results of which are summarized in table 2 . table 2__________________________________________________________________________ blowing base additive agent evaluation items resin ( part ) ( part ) density 1 2 3 4 5 6 7 8__________________________________________________________________________example 2formulation 1 b i 4 . 60 0 . 014 a b b a b a a bformulation 2 b i 2 . 9 0 . 077 a b b a a a a aformulation 3 b i 1 . 5 0 . 174 a a a a a a a areference 2formulation 1 * b none 60 0 . 080 d d d d a d d bformulation 2 * b none 9 0 . 089 c c d d a d b bformulation 3 * b none 5 0 . 195 b c c c a d c d__________________________________________________________________________ * not an example of the invention . evaluation item 1 compressive strength coefficient ; 2 50 % compression permanent set ; 3 compressive creep ; 4 surface smoothness ; 5 feedability through extruder ; 6 maximum shrinkage ; 7 dimensional stability ; and 8 water absorption ratio . the olefin polymer resin a was mixed and kneaded with 0 . 3 percent dicumyl peroxide as a cross - linking agent and 1 . 5 percent of the additive i to obtain a crosslinked polyethylene resin ( in the form of beads having an average diameter of about 1 . 2 mm ) having a gel ratio of about 60 percent . the beads were impregnated , in a pressure vessel , with dichlorodifluoromethane under increased pressure and heat and then cooled to obtain expandable crosslinked polyethylene beads containing 14 percent of dichlorodifluoromethane . the resulting expandable beads were then heated by steaming with 0 . 23 kg / cm 2 g ( 22 . 6 kpa ) steam for 45 sec . and the resultant primary expanded beads had a substantially uniform density distribution of about 90 kg / m 3 . thereafter , the primary expanded beads were heated in a pressure vessel at 80 ° c . for 15 hours while being pressurized by compressed air of 10 kg / cm 2 g ( 981 kpa ). then , steam of 0 . 32 kg / cm 2 g ( 31 . 4 kpa ) was blown over the beads to give secondary expanded beads having a density of 25 kg / m 3 . the resultant secondary expanded beads , as pressurized by compressed air of 1 . 5 kg / cm 2 g ( 147 kpa ), were charged in a mold of a press molding maching ( model echo - 120 manufactured by toyo machinery & amp ; metal co ., ltd .) and the mold was heated by steam of 1 . 2 kg / cm 2 ( 118 kpa ) to obtain a molded article . the molded article had a density of 31 kg / m 3 and showed good fusion between beads . the water absorption ratio of the molded article was less than 0 . 01 g / cm 3 . except that the additive i was not used , the same procedure and conditions as those used in example 3 were repeated to obtain the primary and secondary expanded beads ;, which had densities of 110 kg / m 3 and 30 kg / m 3 , respectively . these primary and secondary expanded beads showed a considerable shrinkage and were replete with surface wrinkles , as compared with those obtained in example 3 . in addition , the blowing agent - impregnated expandable beads of reference 3 , had a useful life of only 20 minutes which was substantially shorter than that observed for the expandable beads of example 3 ( 6 hours ). further , the molded articles obtained in reference 3 showed a higher water absorption ratio ( 0 . 015 gm / cm 3 ) as compared with example 3 , and its shock - absorbing properties and mechanical properties were significantly inferior to those achieved in example 3 .