Crystallization of isotactic polypropylene : the influence of stereo-defects Citation for published version (APA): Burgt, van der, F. P. T. J. (2002). Crystallization of isotactic polypropylene : the influence of stereo-defects. Technische Universiteit Eindhoven. https://doi.org/10.6100/IR559498 DOI: 10.6100/IR559498 Document status and date: Published: 01/01/2002 Document Version: Publisher’s PDF, also known as Version of Record (includes final page, issue and volume numbers) Please check the document version of this publication: • A submitted manuscript is the version of the article upon submission and before peer-review. There can be important differences between the submitted version and the official published version of record. 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Proefschrift. - ISBN 90-386-2674-6 NUR 952 Trefwoorden: polymeren; reologie / polymeerstructuur / kristallisatie / polyolefinen; isotactisch polypropylene / tacticiteit / polymerisatiekatalysatoren / Ziegler-Natta / metallocenen Subject headings: polymers; rheology / polymer morphology / crystallization / polyolefins; isotactic polypropylene / tacticity / polymerization catalysts / Ziegler-Natta / metallocenes Printed by the University Press Facilities, Eindhoven, the Netherlands. This research was financially supported by the Dutch Polymer Institute (DPI; pro- ject #132). Crystallization of isotactic polypropylene The influence of stereo-defects PROEFSCHRIFT ter verkrijging van de graad van doctor aan de Technische Universiteit Eindhoven, op gezag van de Rector Magnificus, prof.dr. R.A. van Santen, voor een commissie aangewezen door het College voor Promoties in het openbaar te verdedigen op woensdag 20 november 2002 om 16.00 uur door Frank Peter Theodorus Johannes van der Burgt geboren te Eindhoven Dit proefschrift is goedgekeurd door de promotoren: prof.dr. P.J. Lemstra en prof.dr.ir. W.H. de Jeu Copromotor: dr. S. Rastogi Dedicated to Arend Eshuis y 7 December 1999 Contents Summary xi 1 Introduction 1 1.1 Polypropylene . 1 1.1.1 History . 1 1.1.2 Properties and economic relevance . 1 1.1.3 Development of metallocene catalysis . 2 1.2 Stereo-isomerism and stereo-regularity . 2 1.3 Catalysis and stereo-defect distribution . 4 1.3.1 Single stereo-defects . 4 1.3.2 Stereo-defect distribution . 5 1.4 The outline of the thesis . 6 2 Experimental methods 7 2.1 Introduction . 7 2.2 Electron microscopy and thin film preparation . 7 2.3 Differential scanning calorimetry . 8 2.4 Wide-angle x-ray scattering . 8 2.4.1 Subtraction of the amorphous halo . 9 2.4.2 Determining the ratio / ¡ phase . 10 2.5 High-pressure treatment . 11 2.6 Rheometry . 11 2.6.1 Melt characterization . 12 2.6.2 Crystallization experiments . 12 3 Polymorphism in polypropylene 13 3.1 The phase . 13 3.1.1 The crystal structure . 13 3.1.2 Crosshatched lamellae . 15 3.2 The ¢ phase . 15 3.3 The ¡ phase . 15 3.3.1 The crystal structure . 16 3.3.2 Morphological features . 16 viii Contents 3.4 Pressure treatment . 16 3.5 Useful data on polymorphism . 17 4 Crystallization of metallocene derived polypropylenes 21 4.1 Introduction . 21 4.2 Materials . 21 4.3 Ambient conditions . 22 4.3.1 Morphology . 22 4.3.2 Differential scanning calorimetry . 24 4.3.3 Wide-angle x-ray scattering . 26 4.4 High Pressure studies . 29 4.4.1 High pressure crystallization . 29 4.4.2 In-situ high pressure experiments . 29 4.5 Discussion . 34 4.5.1 Crystal structure and morphology . 34 4.5.2 Polymorphism . 36 4.5.3 High pressure crystallization . 39 4.6 Conclusions . 40 5 Crystallization of Ziegler-Natta derived polypropylenes 43 5.1 Introduction . 43 5.2 Materials . 43 5.3 Ambient Conditions . 44 5.3.1 Microscopy . 44 5.3.2 Differential scanning calorimetry . 44 5.3.3 Wide-angle x-ray scattering . 47 5.4 High-pressure studies . 48 5.4.1 High-pressure crystallization . 48 5.4.2 In-situ high-pressure experiments . 50 5.5 Discussion . 51 5.6 Conclusions . 55 6 Metallocene versus Ziegler-Natta derived polypropylenes 57 6.1 Introduction . 57 6.2 Morphology . 57 6.3 Melting temperatures . 58 6.4 Crystallinity and polymorphism . 61 6.4.1 (hkl) reflections of the phase and isotactic perfection . 61 6.4.2 Polymorphism versus tacticity . 61 6.4.3 Crystallinity versus tacticity . 62 6.4.4 Pressure influence and growth direction . 62 6.5 Modelling with disordered structures . 63 6.5.1 Model of disordered structures . 63 Contents ix 6.5.2 Method of calculation of the x-ray diffraction patterns . 65 6.5.3 Results of the calculations . 66 6.6 Line broadening analysis . 70 6.7 Conclusions . 71 7 Correlation of molecular structure and rheological parameters 73 7.1 Introduction . 73 7.2 Theoretical aspects . 74 7.2.1 Moments of the molecular weight distribution . 74 7.2.2 The Cross model . 75 7.2.3 The polydispersity index . 76 7.2.4 The Maxwell relaxation-time spectrum . 76 ¦¨§ 7.2.5 £¥¤ versus . 77 7.2.6 The plateau modulus . 77 7.3 Influence of molecular weight distribution . 78 7.3.1 The storage and loss modulus. 79 7.3.2 The complex dynamic viscosity. 79 7.3.3 The Cross model . 80 7.3.4 The polydispersity index . 82 7.3.5 The Maxwell relaxation-time spectrum . 82 7.4 Influence of molecular weight . 85 ¦¨§ 7.4.1 £¥¤ versus . 85 7.4.2 Small MwD differences in metallocene samples . 86 7.5 General Correlations . 87 7.5.1 Correlation between © and . 87 £ ¤ 7.5.2 Molecular weight distribution dependency on © and . 88 7.5.3 The plateau modulus . 88 7.6 Example: Influence of molecular weight distribution on crystal- lization . 90 7.7 Conclusions . 93 A Shift-factors and simple constitutive equations 95 A.1 Shift factor and WLF-fits . 95 A.2 Data-fitting with simple constitutive equations . 96 A.3 Relaxation-time spectra . 97 Bibliography 99 Technology assessment 107 Samenvatting 109 Acknowledgements 111 x Contents Curriculum Vitae 113 Summary Polypropylene (PP) was discovered in the early 1950s. Since then PP has grown to a commodity polymer with numerous grades for specific end uses. By con- trolling the polymer chemistry it is now feasible to generate a range of poly- propylenes possessing mechanical properties varying from a thermoplast to an elastomer. Stereo-regularity and its distribution along the chain play a crucial role in the development of these polymers. The degree of stereo-regularity as well as the stereo-defect distribution of poly- propylene are strongly dependent on the catalyst and on the polymerization con- ditions. In this thesis we have investigated the crystallization behavior of iPPs with varying isotacticity as a function of the stereo-defect distribution based on the origin of the catalyst. More specifically, Ziegler-Natta catalysts introduce a block-like distribution of stereo-defects, and the samples used derived from metallocene catalysis, yielded a random distribution. For this purpose various techniques were used, such as: wide-angle x-ray scattering, electron microscopy, differential scanning calorimetry and rheometry. With respect to crystallization behavior it was observed that for both molecular structures an increasing amount of stereo-defects suppresses the crystallinity and gives rise to larger amounts of the ¡ polymorph, especially on slow cooling. The metallocene derived iPPs show a stronger dependence on the stereo-defects com- pared to the Ziegler-Natta derived materials. Differences in molecular structure are displayed in the melting temperatures which are for Ziegler-Natta derived iPP structurally higher compared to the metallocene samples. The morphologies observed for Ziegler-Natta derived iPP are rather similar to those presented in literature. For example in stereo-irregular Ziegler-Natta samples an overgrowth of the lamellae with ¡ phase is observed. However, metallocene samples show considerable morphological variations with varying tacticity. In poorly isotac- tic metallocene PP curved lamellar morphologies are observed which may be caused by incorporation of a part of randomly distributed stereo-defects within the crystal lattice. After solid state analysis of various polypropylenes, the behavior in the melt was investigated. Different catalysts systems, especially in Ziegler-Natta cataly- sis, can also yield different molecular weight distribution or, for example add a xii Summary high molecular weight tail to the distribution.