A new method of estim ati ng t he eq uiIibrium melting tem perature, T m, of a poIy mer is descr,lbed, and appli ed to polychIorotnfiuoroethylene (P CTFE) , Experim entall y determll1~d values of the sO,-called obser ved melting point, T ~ C obs), a re plotted as a function of t he Isother,mal crystalIl zatlOn temperat ure, 'l'x. , . \'\Then frced of scconda ry effects, s uch as recrystaIIIzatlOll, the data ~t a s t ra lgh t lille of posit ive s lope on a T~(obs) versus T x plot, '1', be~n g t~e abscIssa. This 1m? I~ t hen extrap o~~ted ~o ,its intersection wi th t he line '1'~ (obs) = T x , ~he te mperat ure at t hi s In te rsectIOn IS 7 m' 1hls Intersection is at 224°C for PCTF E a nd T m IS quoted as 224 ± 1°C, (The hi ghest melti ng po i nt act ua lI y attain ed for a speci m e l~ was 218,2 00.,) The v,alue of '1'", estim ated usin g t he extrapolation procedure is co mpa rcd WIth t hat estll;, ated USll1 g th e customary method of slow st epwise warming, A theorctlcal Just lfi catlOll IS gIven [or making t he type o f plot mentioncd abo\'e, The most Imp or~an t ass ump t Ion used in the theo ry is t hat on(' of the dim e nsions of the growin g crystal retains a val,ue r ather close to t hat of t ho app ropri ate growth llu cleus during a n isot hermal ~r y s ta lll zatlOn, the other two dimenSion s bCll1g Ia rge in comparison, Combin ation of th IS WIth the fact t hat t hc r cleva nt dimension of th e growth nu cle us will var v as the reciprocal of t he d egree, of s upcrcooIing lead s to the prediction of melting points t llat inc rease 1ll1early With crystallizatIOn te mperat ure, The ass ump tion t hat ono of the dimension s of the crystal retains a valu e fairly cIose t

(I) The requirements for making a critical test of whether two- or three-dimensional surface nucleation controls the radial growth of lamellar spherulites in bulk are discussed. Radial-growth-rate data were obtained on spherulites of polychlorotrifluroethylene (PCTFE) for a wide range of supercooling ΔT, and found to agree with a growth-rate law based on coherent two-dimensional surface nucleation, viz., G=G0 exp(—ΔF*/RT) exp[—Kg/T2(ΔT)]. Approximations for ΔF* are given. (II) Parameters related to the recently proposed ``kinetic'' viewpoint of homogeneous nucleation and growth of lamellar polymer crystals with chain folds are obtained. The nucleation constant Kg is analyzed to obtain σσe=184 erg2/cm4[σ is the lateral surface free energy, σe is the end (chain-folded) surface free energy]. A similar value of σσe is obtained from bulk-crystallization studies. The homogeneous nucleation process was identified at ΔTh=70°C, and a value of σ2σe=950 erg3/cm6 calculated from Kh in I=(NkT/h) exp(—ΔF*)exp[—Kh/T3(ΔT)2]. Combination of σ2σe and σσe gives σ=5.2 erg/cm2 and σe=36 erg/cm2, the latter corresponding to a work on chain folding, q, of 3.8 kcal/mole of folds. A value of σ=5.4 erg/cm2 is obtained independently using an empirical method. Further, an independent estimate of σe∼35 erg/cm2 is obtained for PCTFE from electron-microscope studies of the lamellar thickness, after accounting for the increase of thickness resulting from segmental mobility that occurs subsequent to initial growth using melting-point data. The over-all role of q in homogeneous nucleation and growth in linear polymers is discussed in terms of a reduced variable treatment using PCTFE and polyethylene as examples. The ``kinetic'' chain-fold theory gives a consistent picture of surface free energies, rates of homogeneous nucleation and growth, melting behavior, and the variation of initial step height with temperature. (III) A discussion is given concerning the shape of the bulk-crystallization isotherms associated with spherulitic growth, including stage-1 and stage-2 crystallization, and the presence of amorphous material in the spherulites.

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\ Vh e n s u bcooled fro m the m elt to any tempera t ure between abou t 90 t o lJ 0 °C, polybu te l1!'-l tra nsform s at a r eadily m eas ura ble rate to a cr ys talline phase de noted "form 2," wh ich is t yp ically sphe ruli t ic. The kinetics of this process have bee n m eas ured by op t ical and d ihtometric t ech ni ques . The r es ults are consistent w ith th e cOlleepts t h a t th e ini tia tion is het erogeneo us, that the in it iation is followed by spherical g row t h (Avrami n = 3), and that t he growth rate is nucleation controlled. Va lu es a rc ob ta in ed for t he s urface fr ee e nergi es and r elated qU:l nt it ies t hat ar c cons is tent with crystalli zation by cha in folding: (J = 7.2 er g/ cm 2 or 7.2 mJ/ m 2 , (J , = 15.5 er g/cm 2 or 15.5 mJ/ m2, a nd wor k of chain folding q= 1.7 X 10-13 ero-/fold. (For comparison, q is 2.1 X 10-13 e rg/fold for polyeth ylene.) The work of ch a in foldin g of polybu te ne-l is also compa red with t hat of polych lor ot rifluoroethy lene, and it is shown t ha t an in crease of q is conn ec Led with a n increase of equi librium me lt ing t cmperat ure. Crys ta l form 2 s ubseque ntly convcr ts s lowly n car room tempcrature to a cr ys t alline phase denoted " form 1" of diffcre nt hcli city a nd d ens ity, and Lh e ratc of t his crystal-crystal t ransform a t ion is also studi cd . The A vrami p ar a meter fo r t he form 2 form 1 process is n = 2. T he process a ppears t o be nucleaLion cont rolled. It is s hown t ha t form 1 is, everywhere below its melting point, t he stable form. The equili brium mel t ing temper ature for form 2 is es t im ated t o be a bou t 128°C, a nd for form 1 a bou t 141 °C . A deg ree of cr ys t allini ty scale bascd on sp cci fic volum e is establis hed. Th e degr ee of crystalli ni ty of form 2 is a bou t 52 per ce nt, a nd a fter convers ion t o form 1, th e crystaJl ini ty is a bout 77 p cr cen t .

The diffrac tion of x-rays by the crystalline n-paraffin s, C36 H ' 4 , C4.H"o, and C". H ",o, was examin e d a t s mall angles -be low se ve n deg re es 2IJ -as a fun c tion of te mp e rature. The Bragg maxima (001) that occ ur at these ang les res ult from a la mell a r re peat di sta nce whic h de pe nd s on th e molec ul a r length. I n ge ne ral the inte nsity of th ese maxim a was found to inc rease with increas ing te mp e rature in a n approximately re versible manne F. All the samp les exp e rie nce d so lid-so lid ph ase tra nsitions in th e te mperature ran ge of observa tion. S eve ral possibl e mecha ni s ms co ns iste nt with th e te mp e rature d e pendence of the inte nsity are considered .