Poli(para-klorostiren) zincirlerinin çeşitli çözücülerde geniş bir sıcaklık bölgesinde dipol momentleri ve intrinsik viskoziteleri

Abstract

Pol i (para-kl oros ti ren) (PPCS) moleküllerinde polar grupların zincire dik olması nedeni ile, ortalama dipol momenti üzerine dışlanmış hacim (excluded volume) etkilerinin bulunmayacağı varsa yılmaktadır. Bu yüzden, molekül içi etkileşmeleri ile çözücü etkilerinin vinil zincirlerinin konformasyonları üzerinde yapacağı değişmeleri araştırmak için PPCS'nin uygun bir polimer olduğu anlaşılmaktadır. Bu çalışmada, PPCS'nin ortalama dipol momentleri, theta(9)- çözücülerde, theta-noktas ı (izopropil benzende 0 = 59 C, n-propil benzende 0=43 C) dolaylarında oldukça geniş bir sıcaklık bölgesin de, benzende ise 15 -70 C arasında ölçüldü. PPCS'nin ortalama di pol momentleri, theta-noktasının altındaki sıcaklıklara gidildikçe küçülmekte, theta-noktasının üstündeki sıcaklıklarda ise pek fazla değişmemektedir. Dipol momentin sıcaklık katsayısı, theta-noktasının altındaki sıcaklıklarda, ortalama d An /dT - (3. 1±0. 2) xl0-3 derece-1 olarak hesaplandı. Bu.sonuçlara dayanılarak theta-noktasının altındaki sıcaklıklarda uzun-mesafe etkileşmelerinin önem kazandığı ve bu yüzden, bu bölgelerde yapılmış dipol moment ölçmelerinin, sadece yakın-mesafe etkileşmelerini yansıtamayacağı ileri sürüldü. PPCS'nin benzendeki dipol momenti değerlerinin ise literatürde verilen sonuçlara uygun olarak, 15 -35 C arasında sıcaklıkla azaldığı, 35 -70 C arasında ise arttığı gözlendi. 2 PPCS zincirleri için, <\ı >/x değerleri ve yeterince. uzun zincirler için D dipol moment oranları, - II - D. = -H-j x "ö hesaplandı. Yapısı PPCS'nin tekrarlanan birimine benzeyen madde olarak p-klorotoluenin dipol momenti aynı' dipolmetrede ölçüldü (benzende, y »1.99D; izopropil benzende, p »1.94D) ve D dipol mo- ment oranlarını hesaplamak için bu değerler kullanıldı. Ayrıca, PPCS'nin benzen, izopropil benzen ve n-propil ben zendeki [n] intrinsik viskozitelerinin sıcaklıkla değişmesi de in celendi. tntrinsik viskozite değerlerinin de theta-cözücülerde, 9-noktasından daha düşük sıcaklıklara gidildikçe küçüldüğü, 8-noktasının üstündeki sıcaklıklarda ise bu düğüsün yavaşladığı gözlendi. İntrinsik viskozite, zincirin uç-son uzaklığı karelerinin ortalaması ile orantılı olduğundan 6-noktasının altındaki sıcaklıklara gidildikçe, polimer zincirinin büzüldüğü gösterildi. PPCS'nin benzendeki intrinsik viskoziteleri de 6.5 -50 C sıcaklık bölgesinde sıcaklıkla düzgün bir şekilde artmaktadır. Bu sistemde, theta-çözücül erinde gözlenen dönüm noktasına rastlanmadı. İntrinsik viskozite ölçümlerinden, polimer çözeltilerinin termodinamiği ve hidrodinamiği üzerinde yapılan çalışmaların so nuçları kullanılarak, polimer-çözücü etkileşme parametres i için yapılan hesapların anlamlı sonuçlar verdiği bulundu.

The probable absence of excluded volume effects on the mean-squared dipole moments of poly (p-chlorostyrene) (PPCS) chains makes this polymer suitable for the investigation of the influence of intramolecular interactions on the confor mations of vinyl polymers. The dipole moment measurements of PPCS were carried out in various solvents and temperatures in this work. The molecular weight of PPCS sample was 2.7x10 in both isopropyl benzene and n-propyl benzene solvents. In benzene solutions the molecular 4 weight of PPCS was 6.5x10. The dielectric constants of these PPCS solutions, were measured by a WTW DM 01 Model dipolcmeter working at a constant 2 MHz. frequency. 2 Mean-squared dipole moment of the chain were calculated by means of the appropriate form of the Guggenheim-Smith equation: 27 kTM, de dn2. x " 47yN(e1 + 2)2 dw2 " dw2 w2"*° where x is the number of repeat units, de/dw, is the rate of change of the dielectric constants (permittivity) E of the solution with the polymer weight fraction w", n is the refractive index of the solution, £. is the dielectric constant of the solvent. N, k, T, M - IV' refer to Avogadro's number, Boltzmann constant, absolute tempera ture and molecular weight of the repeat unit, respectively. Isopropyl benzene and n-propyl benzene are theta(8) -solvents for PPCS at 59 C and 43 C, respectively. By theta-solvent, we mean a solvent where the polymeric chain assumes its unperturbed dimen sions, i.e. the chain is unaffected by long-range interferences such as the excluded volume effect. This situation occurs at a specific temperature known as the theta-temperature of the solvent. The mean-temperature coefficient of the dipole moment of PPCS in these 9-solvents was calculated as d In /dT = (3»l±0.2)xl0~3 degree"1 below the theta-temperatures. The mean-squared dipole moments of PPCS chains were found to exhibit a negligible temperature depen dence above the theta-points. Consequently, it may be considered that the long-range interactions were present below the theta-temperatures and that experimental results in this region did not reflect intramolecular short-range interactions only, but also long-range interactions with excluded volume effects. However, the experiments which carried out at temperatures above the theta-point may reflect short-range intramolecular and solvent interactions. It was found that the dipole moments of PPCS chains decreased in the temperature range 15 to 35 C and increased between 35 to 70 C in benzene solutions. The change of sign of the slope, however not predicted by existing theories. The temperature coefficient of dielectric constant of isopropyl benzene in the 30 -90 C temperature range, was calculated V- j-| = -2.06x10 J degree"1 The corresponding quantity in n-propyl benzene in the 20 -90 C temperature range was.^1 ?= -2.00xl0~3 degree l Dipole moment of p-chl orot o I uene as an analogue of the repeat unit of PPCS was measured using the same DipolemeLer. It was found equal to 1,99 I) at 15, 25, 35 C in benzene and 1. 94 1) at 30, 50, 70 C in isopropyl benzene. Dipole moment of p-chloro toluene did not change with temperature in the above- intervals. These values denoted by U were used in calculating o the dipole moment ratios, D^ for sufficiently long chains, is defined as D" = -iL-2 x »a The dipole moment ratio DM is an important quantity characterizing the polymer conformation. In the present work, the dipole moment ratios of PPCS in benzene, isopropyl benzene and n-propyl benzene were determined over a wide range of temperature and compared with theoretical results. Furthermore, the intrinsic viscosity, [r|], of PPCS chains was measured in isopropyl benzene, n-propyl benzene and benzene, nearly in the same temperature range as the dipole moment measure ments. An Ubbelohde type capillary viscosimeter was used to deter mine the intrinsic viscosity of PPCS. It was calculated according to Huggins equations: c = [n] + k- [n]2c where n denotes the spesific viscosity, c is the polymer - VI concentration in g/dl, k' is the Hugğins constant. According to this equation [n] is evaluated from the intercept by plotting nsp/c vs-c. The increase of the intrinsic viscosity with temperature was more rapid in the region below the theta-temperature compared to that above the theta-temperature, for isopropyl benzene and n-propyl benzene solvents. For theta solvents, a similarity between the intrinsic viscosities and dipole moments for the same tempe rature range was observed. The intrinsic viscosity is proportional to the mean-squared stance, ' «xrV2 2 end-to-end distance, , according to Flory-Fox equation: 21 where $ is a constant of proportionality which was taken as 2.6x10 in calculations and M is the molecular weight of polymer. Consequently, it may be considered that as the temperature decreases the polymer coils contracted below the theta- temperatures more rapidly than that above the theta-temperatur es. The intrinsic viscosity of PFCS in benzene solution increased with constant slope in the interval 6.5°-50°C. The intrinsic viscosity at the theta-temperature is given by [n]6 = K6M1/2 where Kfl is a constant of proportionality depending on the type of polymer. Unperturbed chain dimensions and conformational characte ristics such as the constant, Kfl and characteristic ratio, C,,, may be calculated from the intrinsic viscosity of PPCS at the theta- points.